Conventionally, in pouring and casting molten metal, the immersion nozzle has been used for the purposes of preventing molten-metal oxidation, nonmetallic-inclusion involvement and occurrence of turbulent flow and splash. The immersion nozzle, because of use under severe conditions that its bore contacts flowing molten metal and the outer surface borders on the ambient air, frequently suffers damages of erosion, fracture or breakage. Meanwhile, the alumina or the like in molten steel adheres and deposits on a bore wall of the immersion nozzle to thereby narrow the molten-steel passage. In a conspicuous case, this causes clogging to forcibly interrupt casting operation. For this reason, where casting is scheduled long in time, it is required to exchange the immersion nozzle in the course of casting. The general exchange method of an immersion nozzle includes, for example, removing the old immersion nozzle in a state that casting is once suspended and the tundish is raised to set up a new immersion nozzle, thereafter resuming the casting.
However, recently there is a demand for the capability of swiftly exchanging an immersion nozzle during casting for the purpose of preventing steel-quality deterioration resulting from casting interruption or troubles induced due to cast resuming. In FIG. 20 is shown, for example, an example of Japanese Utility Model Registration No. 3009112 as an apparatus for swiftly exchanging an immersion nozzle without raising the tundish during continuous casting.
In this example, the immersion nozzle 52 in use is urged upward by the key-plate rows 51 arranged on both sides thereof and held in a state being urged onto a joint surface 54 of an upper nozzle 56. When to exchange the immersion nozzle 52, a new immersion nozzle 52a is pushed out sideways by a pusher 58 coupled to a cylinder 57, thereby exchanging the immersion nozzle 52 in use. At this time, because the new immersion nozzle 52a slides while being urged onto the joint surface 54 of the upper nozzle 56, even during casting the immersion nozzle can be instantaneously exchanged without leaking molten steel.
However, in the exchanging apparatus of this example, the upper nozzle and the immersion nozzle are pressure-joined at refractory joint surfaces thereof. A gap might occur between the joint surfaces due to local wear upon exchange operation, thermal expansion during use or variation in surface accuracy caused in manufacture. The gap if occurred causes deterioration in steel quality due to air suction through the gap or a danger of leak molten steel through the gap. Generally, in the joint surface of an immersion nozzle, joining is made through a seal member for the purpose of preventing such problems and securing sufficient sealability. However, in the exchange apparatus of this example, because the new immersion nozzle slides while being urged on the upper nozzle, the seal member set in the immersion nozzle is possibly chipped off by the upper nozzle. Thus, it is impossible to apply a seal material.
In the pressure-fit supporting apparatus for an immersion nozzle introduced in JP-B-2-49184, upon exchanging an immersion nozzle a new immersion nozzle is horizontally moved with a spacing to a joint surface of the upper refractory and, in a predetermined position, vertically pushed up and held by pressure-joining. In this apparatus, by previously set a seal member on a joint surface of the new immersion nozzle, the seal member can be interposed between the joint surfaces of the immersion nozzle and the upper refractory. However, in this apparatus, the immersion nozzle is supported by a pressure-joined support part of a metal-frame integrated structure to have a structure that, upon exchange, the immersion nozzle much used is first released of pressure-joining force and lowered downward. For this reason, there is a concern on the problems that, where the apparatus is used to exchange an immersion nozzle in casting, steel leaks from the upper refractory or impossible removal of solidified metal suspended around the nozzle bore. Namely, if solidified metal remains around the upper nozzle bore, a gap occurs at a joint surface to a new immersion nozzle or heavy damage is caused in the joint surface. Even in the presence of a seal member, its function is impeded and hence sufficient sealability is made impossible to obtain.
Furthermore, in JP-A-10-99947, in an apparatus for exchanging an immersion nozzle much used by pushing out with a new immersion nozzle, the new immersion nozzle horizontally moves with a spacing to a joint surface of the upper nozzle positioned above until coming to a predetermined position, and is pressure-joined at the predetermined position. Consequently, a seal member can be used. However, in this apparatus, because the loading of pressure-joining force to the immersion nozzle is only at left-and-right one point in a side surface center of the immersion nozzle and the immersion nozzle during parallel movement is ready to incline due to the resistance to or floating force by molten steel, the pressure-joining force is not easily applied evenly onto the entire seal member on the immersion-nozzle joint surface. Thus, there has been a problem of impediment to sealability.